1. Field of the Invention
The present invention relates to document handling systems and, more particularly, to document handling in a duplex imaging system.
2. Brief Description of Related Developments
There have been various approaches in the duplicating and printing field for printing on a first side and a second side of a sheet.
A printing system adapted for use in high speed printing can employ two print engines arranged in tandem. In some instances, the print engines are arranged in straight-line tandem. Each print engine prints on one side of the sheet. In this way, duplex prints are formed. Each print engine may be an electrophotographic print engine. These print engines are generally identical to one another and have a photoconductive member that is charged to a substantial uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of a document being printed. Exposure of the charged photoconductive member effectively dissipates the charge thereon in the irradiated areas to record an electrostatic latent image on the photoconductive member corresponding to the informational areas desired to be printed. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the electrostatic latent image is developed with dry developer material comprising carrier granules having toner particles adhering triboelectrically thereto. However, a liquid developer material may be used as well. The toner particles are attracted to the latent image, forming a visible powder image on the photoconductive surface. After the electrostatic latent image is developed with the toner particles, the toner powder image is transferred to a sheet. Thereafter, the toner powder image is heated to permanently fuse it to the sheet. After the toner powder image has been formed on one side of the sheet, the sheet is advanced to the next print engine to have information printed on the other side thereof. The sheet may be inverted or the print engine may be oriented so as to print on the opposed side of the sheet. In any event, both print engines are substantially identical to one another and produce a sheet having information on opposite sides thereof, i.e., a duplex sheet. This is duplex printing. While electrophotographic print engines may be utilized, one skilled in the art will appreciate that any other type of print engine may also be used. For example, ink jet print engines, or lithographic print engines may be used. Furthermore, these print engines may be mixed and matched. Thus, the printing system does not necessarily require only electrophotographic print engines or only ink jet print engines or only lithographic print engines, but rather may have an electrophotographic print engine and an ink jet print engine, or any such combination. Another approach has been to provide a sheet handling mechanism for inverting a sheet within one print engine so as to form duplex prints as an output therefrom. Such machines are more compact than the tandem arrangement.
The following disclosures appear to be relevant to printing system using tandem print engines: U.S. Pat. No. 5,568,246; Patentee: Keller, et al.; Issued: Oct. 22, 1996; U.S. Pat. No. 5,598,257; Patentee: Keller, et al.; Issued: Jan. 28, 1997; U.S. Pat. No. 5,730,535; Patentee: Keller, et al.; Issued: Mar. 24, 1998.
The references cited, U.S. Pat. Nos. 5,568,246, 5,598,257; and 5,730,535, disclose a printing system including two print engines arranged in tandem. Each print engine includes an inverter. The print engines are electrophotographic printing machines.
In the description herein the term xe2x80x9csheetxe2x80x9d generally refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopyxe2x80x9d. A xe2x80x9cjobxe2x80x9d is normally a set of related sheets, usually a collated copy set copied from a set of original document sheets or electronic document page images, from a particular user, or otherwise related. Simplex documents have images on only one side and a duplex document has images on both sides.
In a first aspect, the disclosed embodiments are directed to a method of duplex imaging in a tandem print engine system. The features of the disclosed embodiments include imaging a first side of a sheet in a first marking module in the system, inverting the sheet, and imaging a second side of the sheet in a second marking module in the system one pitch after N revolutions of a photoreceptor following the first side imaging.
In another aspect, the features of the disclosed embodiments are directed to a method of duplex imaging in a single print engine electrophotographic system. The method of this embodiment includes imaging a first side of a sheet, inverting the sheet, and imaging a duplex side of the sheet one pitch after an integer number of revolutions of a photoreceptor in the system.
In a further aspect, the features of the disclosed embodiments are directed to an electrographic printing system. The features of this embodiment include a tandem print engine system including a first photoreceptor and a second photoreceptor. The first and second photoreceptor each have seams that are offset by an amount X relative to each other. Each of the first and second photoreceptors are revolving at a constant speed wherein an imaging of a duplex side of a sheet occurs an (N+X) number of revolutions and one pitch after imaging of a simplex side of the sheet. N is an integer number of revolutions of the first and second photoreceptor and X is any real number.
In yet another aspect, the disclosed embodiments are directed to a computer program product. Features of this embodiment include a computer useable medium having computer readable code means embodied therein for causing a computer to perform duplex imaging in a tandem print engine system. The computer readable code means in the computer program product comprise computer readable program code means for causing a computer to image a first side of a sheet in a first marking module in the system, computer readable program code means for causing a computer to invert the sheet, and computer readable program code means for causing a computer to image a second side of the sheet in a second marking module in the system one pitch after N revolutions of a photoreceptor following the first side imaging.